One of core components of an electric vehicle is battery. Some electric vehicles use lithium ion batteries. Performance of a lithium ion battery is generally poor at a low temperature. Thus, it is required to heat the lithium ion battery. An electric vehicle battery heating system has become a technical challenge. An in-series IGBT (insulated gate bipolar transistor) heating is one of conventional methods for heating an electric vehicle battery.
Because electric vehicle batteries are mostly configured in series to form a battery pack, for the IGBT heating, the IGBT is connected with the battery pack in series, and the battery pack is heated via a pulse current which is generated by an instant short circuit of the entire battery pack. If a performance of the battery is poor, a pulse short circuit current may not be overlarge (for instance, less than 3000 A) because of a large resistance of the battery, thus an entire pack in-series IGBT heating is feasible. However, with an improvement of the performance of the battery, the resistance of the battery is greatly decreased so that the pulse short circuit current of a hybrid vehicle battery pack may be 5000 A, and that of a pure electric vehicle battery pack may be 7000 A, which are too large for the IGBT, a fuse plug and the battery itself.
In addition, on one hand, because the battery pack generally includes hundreds of batteries connected in series, a non-uniform discharge of each single battery may be caused during a repeated charge-discharge process, which may cause a capacity loss of the battery pack; and on the other hand, for the in-series IGBT heating, a discharge difference may be caused because of different battery groups, thus a voltage difference of the battery pack may be caused accordingly.